A DYNAMIC FRICTION MODEL FOR REACTION WHEELS

This paper addresses the problem of the bearing friction in a reaction wheel and applies a dynamic friction model in the current control loop. The dynamic friction model assumes that there are elastic bristles in the contact surfaces that bends when slipping forces are applied. The bristle behavior mimics the Stribeck effect without discontinuities. Some experiments were carried out in order to collect the necessary data to estimate the model parameters, using different control profiles in both current and velocity so as to emphasize a particular parameter. Least squares curve fitting was firstly employed to obtain viscous and Coulomb friction coefficients, while a Kalman filter estimated the break-away torque for a Stribeck friction model as well as viscous and Coulomb. Finally an Extended Kalman Filter (EKF) was used to obtain some parameters of a LuGre dynamic friction model. Results of the filtering process are presented, thus asserting that dynamic friction models can be estimated with EKF provided the necessary conditions for sensor accuracy are met.